Journal of the American Chemical Society p. 4715 - 4720 (1985)
Update date:2022-08-11
Topics:
Grunwald, Ernest
Previous theory of structure-energy relations is extended to mechanisms with three concerted reaction events.Data for 25 reactions (five alcohols, five acid catalysts) are examined on the basis of four different mechanisms.Only one of the mechanisms fits well.It involves concerted C...O bond formation, proton donation by the acid catalyst, and proton acceptance by a water molecule, according to H2O + HOCH2R + H2C=O + HOOCCH2R' -> H2OH(+) + RCH2OCH2OH + (-)OOCCH2R'.The fit for this mechanism is decisively good in three practically independent tests.The contrast between the present mechanism and that which fits the base-catalyzed reaction (which does not involve HOH as a reagent) can be explained as due to peculiarities of relative acid-base properties of RCH2OCH2OH and H2O.No inconsistency appears with other data.Transition-state coordinates for the acid-catalyzed reaction are tabulated.Progress of C...O bond formation, though variable within the reaction series, is well ahead of that of the proton transfers.Further analysis of the theoretical free-energy surfaces indicates that disparity of progress of the concerted reaction events reaches a maximum at the transition state.
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